CONTACT: JENNIFER CRONIN
2130 Medical Laboratories
Iowa City IA 52242
(319) 335-5661; fax (319) 335-9917
Release: March 2, 1999
UI researcher finding ways to make cochlear implants better mimic
IOWA CITY, Iowa -- Although cochlear implants have opened up the world
of sound for many individuals with profound hearing loss or deafness, the
devices fall short of replicating the normal hearing process.
But that could soon change.
Using a computer model, Jay Rubinstein, M.D, Ph.D., a University of
Iowa assistant professor of otolaryngology, and physiology and biophysics,
has found a way to better mimic the natural spontaneous activity of the
normal cochlea, which could lead to improved hearing for people who rely
on cochlear implants.
Rubinstein, who figured out how to reprogram existing devices, soon
will begin trials on qualified UI Hospitals and Clinics' patients already
implanted with cochlear devices. An initial test of a reprogrammed implant
in a North Carolina patient provided promising data, Rubinstein said. The
UI Research Foundation has applied for a patent for Rubinstein's strategy.
"While much work remains to be done in humans, our laboratory studies
suggest that substantial improvements in all types of sound coding may
be possible, even with the limitations of currently implanted devices,"
In normal hearing, sound waves excite the hair cells in the ear. These
cells then convert the sound into an electrical signal that stimulates
the primary auditory neurons to send the information from the inner ear's
cochlea to the auditory brain stem. The hearing process is impaired in
people who have lost some hair cells. Those with no hair cells at all are
deaf because the hearing process cannot even start.
A cochlear implant is an electronic device that a doctor surgically
places in a deaf person's cochlea. The device, which receives signals from
a processor worn outside the body, acts as the hair cells, converting acoustic
information into electrical signals that can be transmitted to the brain
and perceived as sound.
Although the cochlear implant is supposed to mimic the normal hearing
process, the electrically stimulated auditory neuron responses are substantially
different from acoustically stimulated responses in the normal hearing
ear. The device's electrical stimulation produces highly synchronized activity
across all the neurons, meaning the response is the same for all the neurons.
Acoustic stimulation produces much less across-neuron synchrony, meaning
each neuron's response is independent. This independence allows for much
richer, more detailed sound.
Rubinstein wanted to find a way to recreate the desynchronized, natural
process of normal acoustic stimulation. By increasing the rate of the signal
pulses from the external processor, Rubinstein, in his model, was able
to produce more independent neuron activity. Animal studies performed at
the UI support the predictions of Rubinstein's calculations. Individuals
involved in the animal studies included Paul Abbas, Ph.D., professor of
otolaryngology, and speech pathology and audiology; Charles Miller, Ph.D.,
assistant research scientist in the department of otolaryngology; and Akihiro
Matsuoka , M.D., Ph.D., research assistant in the department of otolaryngology.
Earlier work performed by Blake Wilson at the Research Triangle Institute
in North Carolina, a close collaborator with the UI Cochlear Implant Clinical
Research Center, suggested that coding speech at high signal rates would
reduce neural synchronization.
"Our work demonstrated precisely how those beneficial effects could
be exploited to partially mimic the function of the normal auditory system,"
If upcoming human trials are successful, a limited version of the new
speech processing strategy is possible using currently implanted devices.
These improved versions could be available to UI research subjects within
months, Rubinstein said. U.S. Food and Drug Administration approval would
be necessary prior to more widespread use. A complete implementation of
the algorithm is beyond the capabilities of even the most sophisticated
cochlear implants available today but will be possible using devices that
the manufacturers will make available in the next few years, Rubinstein